The present invention relates to an image forming apparatus such as copy machine, printer and facsimile. In particular, the present invention relates to an image forming apparatus in which an image is formed on an image bearing member and then transferred to a recording medium or sheet.
Conventionally, there has been known an electrophotographic image forming device which, for providing an resultant image with a higher quality, uses a developer mixed with a great amount of additive of inorganic material. In particular, the additive is preferably used in a full color copy machine and printer. Indeed, the existence of the additive provides the developer with a uniform mixing thereof, a ready adherence thereof to the electrostatic latent image on the photosensitive member, a ready transference thereof from the photosensitive member to an image bearing member and an improved collectivity thereof from the photosensitive drum by a scraping blade.
It is preferable that the additive is added as much as possible in order to improve the mixing, developing and transferring properties of the developer. On the other hand, the amount of the additive to be added to the developer should be controlled. That is, an excessive adding of the additive increases the amount thereof that unavoidably moves past a contact region between the blade and the photosensitive member. This causes a part of the additive to be forced and applied onto the photosensitive member, which in turn results in noises in the resultant image and then degrading the same. An insufficient adding of the additive fails to form a stationary remaining thereof adjacent to the contact region of the blade and the photosensitive member, which decreases a collecting efficiency of developer from the photosensitive member. This results in defects in the resultant image, especially in the solid image.
To overcome these problems, U.S. Pat. No. 5,220,390 discloses an image forming device which includes a transfer station where a toner image is transferred from the photosensitive member to the sheet substrate, a cleaning station where the toner that has not been transferred to the sheet substrate is collected by the blade and a cleaning agent supply station where a cleaning agent (e.g., strontium titanate) is provided to the photosensitive member for improving the collectivity of the additive by the blade.
The disclosed image forming device requires a certain space around the photosensitive member that is exclusively occupied by the cleaning agent supply station. Disadvantageously, this increases a size of the photosensitive member. Particularly, for the full color image forming device which includes several photosensitive members for respective color toners, the size of the image forming device will be increased considerably if the cleaning agent supply station is added to each photosensitive member.
In addition, from tests made by the inventors of the present invention, it has been found that the additive includes not only particles effective for cleaning the toner but also particles ineffective therefor, and the effective particles are those charged to the same polarity as the toner while ineffective particles are those charged to opposite polarity.